checkuser.java

一个简单的学生信息查询系统

//CheckUser.java 

import java.sql.*; 

public class CheckUser { 

    // 连接数据库 
    public CheckUser() { 
        try { 
            Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver"); 
        } catch (ClassNotFoundException e) { 
            System.out.println("连接数据库错误" + e); 
        } 
    } 

    // 判断用户名和密码是否合法 
    public boolean isValidUser(String username, String password) { 
        boolean isValid = false; 
        String url = "jdbc:microsoft:sqlserver://localhost:1433;User=sa;Password=;DatabaseName=student"; 
        Connection con = null; 
        Statement stmt = null; 
        ResultSet rs = null; 
        String isValidStr = new String("select * from users where Username='" + username + "' and " + "Password='" + password + "'"); 
        try { 
            con = DriverManager.getConnection(url); 
            stmt = con.createStatement(); 
            // 查询所输入的用户名和密码是否存在 
            rs = stmt.executeQuery(isValidStr); 
            if (rs.next()) { 
                isValid = true; 
            } 
        } catch (SQLException e) { 
        System.out.println("查询数据库错误" + e); 
    } finally { 
        if (rs != null) { 
            try { 
                rs.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
        } 
    } 
    return isValid; 
} 

// 获取用户类型 
public int getUserType(String username) { 
    int flag = 1; 
    String url = "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=student"; 
    String user = "sa"; 
    String pw = ""; 
    Connection con = null; 
    Statement stmt = null; 
    ResultSet rs = null; 
    String userTypeStr = new String("select * from users where Username='" + username + "'"); 
    try { 
        con = DriverManager.getConnection(url, user, pw); 
        stmt = con.createStatement(); 
        // 查询所输入的用户名和密码是否存在   
        rs = stmt.executeQuery(userTypeStr); 
        if (rs.next()) { 
            flag = rs.getInt("flag"); 
        } 
    } catch (SQLException e) { 
        System.out.println("查询数据库错误" + e); 
    } finally { 
        if (rs != null) { 
            try { 
                rs.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
        } 
    } 
    return flag; 
} 

// 修改密码 
public boolean changepw(String username, String password) { 
    boolean changed = false; 
    String url = "jdbc:microsoft:sqlserver://localhost:1433;User=sa;Password=;DatabaseName=student"; 
    Connection con = null; 
    Statement stmt = null; 
    String changepwStr = new String("update users set Password='" + password + "' where Username='" + username + "'"); 
    try { 
        con = DriverManager.getConnection(url); 
        stmt = con.createStatement(); 
        // 修改密码 
        stmt.executeUpdate(changepwStr); 
        changed = true; 

    } catch (SQLException e) { 
        System.out.println("修改密码" + e); 
    } finally { 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
         } 
    } 
    return changed; 
} 

// 添加用户 
public boolean adduser(String username, String password) { 
    boolean add = false; 
    String url = "jdbc:microsoft:sqlserver://localhost:1433;User=sa;Password=;DatabaseName=student"; 
    Connection con = null; 
    Statement stmt = null; 
    String adduserStr = new String("insert into Users values('" + username + "','" + password + "'" + ",'1')"); 
    try { 
        con = DriverManager.getConnection(url); 
        stmt = con.createStatement(); 
        // 添加用户 
        stmt.executeUpdate(adduserStr); 
        add = true; 

    } catch (SQLException e) { 
        System.out.println("添加用户" + e); 
    } finally { 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
        } 
    } 
    return add; 
} 

// 删除用户 
public boolean deluser(String username) { 
    boolean del = false; 
    String url = "jdbc:microsoft:sqlserver://localhost:1433;User=sa;Password=;DatabaseName=student"; 
    Connection con = null; 
    Statement stmt = null; 
    String deluserStr = new String("delete from Users where Username='" + username + "'"); 
    try { 
        con = DriverManager.getConnection(url); 
        stmt = con.createStatement(); 
        // 删除用户 
        stmt.executeUpdate(deluserStr); 
        del = true; 

    } catch (SQLException e) { 
        System.out.println("删除用户" + e); 
    } finally { 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
        } 
    } 
    return del; 
} 

public boolean isExist(String username) { 
    boolean isexist = false;  
    String url = "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=student"; 
    String user = "sa"; 
    String pw = ""; 
    Connection con = null; 
    Statement stmt = null; 
    ResultSet rs = null; 
    String isExistStr = new String("select * from users where Username='" + username + "'"); 
    try { 
        con = DriverManager.getConnection(url, user, pw); 
        stmt = con.createStatement(); 
        // 查询所输入的用户名 
        rs = stmt.executeQuery(isExistStr); 
        if (rs.next()) { 
            isexist = true; 
        } 
    } catch (SQLException e) { 
        System.out.println("查询数据库错误" + e); 
    } finally { 
        if (rs != null) { 
            try { 
                rs.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (stmt != null) { 
            try { 
                stmt.close(); 
            } catch (SQLException ex) { 
            } 
        } 
        if (con != null) { 
            try { 
                con.close(); 
            } catch (SQLException ex) { 
            } 
        } 
    } 
    return isexist; 
} 
}